The nationwide security dragnet involves more than 50,000 trucking companies carrying everything from chemicals used to make soap to gasoline and fertilizer, as well as a review of 2.5 million commercial driver's licenses.

On any given day as many as 76,000 tanker trucks with millions of pounds of hazardous cargo traverse the nation, according to industry estimates. For many of these products, release in a crowded area could be deadly.

"Everything is being looked at a lot harder," said John Conley, vice president of the National Tank Truck Carriers, which represents 200 companies that haul some of the most dangerous cargo.